Homoleptic Rare-Earth Aryloxide Based Lewis Pairs for Polymerization of Conjugated Polar Alkenes

An efficient Lewis pair polymerization of conjugated polar alkenes utilizing simple, homoleptic rare-earth aryloxides with a combination of phosphines and N-heterocyclic carbenes was developed. The polymerizations were found to be active for Lewis acids across the full range of rare-earth metals, and the catalytic activities were observed to be dependent on the ionic radii of the rare-earth metals and the steric and electronic profiles of the Lewis bases. For the methyl methacrylate polymerization, a syndiotactic polymer was produced with an rr value of up to 85%. This rare-earth Lewis pair polymerization system was also found to be effective on more challenging acrylates and acrylamide monomers, such as tert-butyl methacrylate, furfuryl methacrylate, and N,N-dimethylacrylamide. In the case of furfuryl methacrylate, the polymerization proceeded in a controlled manner with a high initiation efficiency. FLP-type addition was confirmed as the initiating step by stoichiometric reactions producing the zwitterionic active species and an end-group analysis.